Method of peeling off chips using peeling plate with integrally formed first and second protrusions

ABSTRACT

A chip peeling apparatus has a plurality of protrusions which include first protrusions and second protrusions lower than the first protrusions. A vacuum pump communicates through holes with grooves defined between adjacent ones of the protrusions. A UV sheet is attached to chips, and the chips are supported in the vicinity of their corners by the tops of the first protrusions. When the vacuum pump is actuated, the chips and streets disposed between the chips are lowered, and the chips are curved and supported in abutment against the tops of the second protrusions. Each of the chips is gradually peeled off the UV sheet under a force tending to recover the original shape of the curved sheet. The chip peeling apparatus is effective in preventing the chips from being damaged and positionally deviated when the chips are attracted and carried.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of and an apparatus forpeeling chips fabricated on a wafer of silicon or the like off a sheetattached to the reverse side of the wafer in a process of manufacturingICs or the like.

2. Description of the Related Art

FIG. 10 of the accompanying drawings shows a conventional chip peelingapparatus 10. As shown in FIG. 10, the conventional chip peelingapparatus 10 includes a base 12 having a hole 16 defined therein whichis connected to a first vacuum source (not shown). A tubular member 18has an end fitted in an upper open end of the hole 16 and a flange 20projecting radially outwardly from an outer circumferential surfacethereof. The flange 20 is fixedly mounted on the end of the base 12which defines the upper open end of the hole 16, thereby supporting thetubular member 18 on the base 12. A cylindrical member 22 is inserted inthe hole 16 and has an outer wall surface and a distal end spaced froman inner wall surface of the tubular member 18 which defines a hole 24therein. A pin 26 is inserted in the cylindrical member 22 for axialsliding movement in the cylindrical member 22, and supports a pluralityof needles 28 mounted upwardly on a distal end of of the tubular member18 and fixed to the tubular member 18 by a cover 32. The suction nozzle30 has a plurality of holes 34 defined therein for insertion of theneedles 28.

A seat 36 is positioned in upwardly spaced relation to the base 12, andthe suction nozzle 30 has a distal end projecting upwardly slightly froma hole 37 that is defined in the seat 36. A suction head 38 is disposedupwardly of the suction nozzle 30 for movement toward and away from thesuction nozzle 30. The suction head 38 has an axial hole 40 definedtherein which is connected to a section vacuum source (not shown).

A process of peeling chips 42 such as of ICs or the like fabricated on awafer off a sheet 44 using the chip peeling apparatus 10 will bedescribed below.

As shown in FIG. 10, when the sheet 44 to which the chips 42 areattached is moved to a position above the seat 36 and brought into heldagainst an upper portion of the suction nozzle 30, the sheet 44 iscurved upwardly. When the center of a desired one of the chips 42 isaligned with the center of the suction nozzle 30, the first vacuumsource (not shown) is actuated to attract the sheet 44 to the suctionnozzle 30.

Then, the pin 26 is lifted to cause the needles 28 to pierce and projectthrough the sheet 44, and ascend with the chip 42 placed on the tips ofthe needles 28, as shown in FIG. 11 of the accompanying drawings. Atthis time, since the sheet 44 is attracted to the suction nozzle 30, thechip 42 is peeled off the sheet 44.

Thereafter, the suction head 38 is moved toward the suction nozzle 30and brought into abutment against the chip 42. The second vacuum source(not shown) is actuated to attract the chip 42 off the sheet 44 to thesuction head 38. The chip 42 will then be transferred to anotherlocation.

FIG. 12 of the accompanying drawings shows another conventional chippeeling apparatus 50. As shown in FIG. 12, the conventional chip peelingapparatus 50 includes a peeling base 52 having a plurality ofprotrusions 54 with flat tops, the protrusions 54 having heaters (notshown). The peeling base 52 has grooves 56 each defined between adjacentones of the protrusions 54 and communicating with a hole 58 defined inthe peeling base 52 which is connected to a vacuum source (not shown). Asuction head (not shown) is positioned above one of the grooves 56 formovement toward and away from the peeling base 52.

A sheet 44 with a plurality of chips 42 and streets 59 remaining as cutfragments in gaps between the chips 42 is moved toward a position abovethe peeling base 52 with the chips 42 above the grooves 56. Theprotrusions 54 have been heated by the heater to apply heat to the sheet44, thereby making the sheet 44 stretchable. The vacuum source isactuated to evacuate the grooves 56, whereupon the sheet 44 is stretchedand curved in the direction in which the vacuum is developed, asindicated by the two-dot-and-dash lines. At this time, the chips 42 havetheir peripheral edges supported on the flat tops of the protrusions 54,and the sheet 44 is peeled off central regions of the chips 42.

Then, the suction head (not shown) is moved toward a desired one of thechips 42. Because of an attracting action of the suction head, the sheet44 is peeled off the peripheral edges of the chip 42, which is attractedto and held by the suction head. The chip 42 will then be transferred toanother location.

The former chip peeling apparatus 10 is disadvantageous in that the tipsof the needles 28 tend to damage the surface of the chip 42. When theneedles 28 are elevated, the sheet 44 itself may also be stretched andlifted. At this time, the needles 28 may not pierce the sheet 44, andhence may not form holes in the sheet 44, with the result that the chip44 may not be separated from the sheet 44.

The latter chip peeling apparatus 50 is also problematic in that whenthe sheet 44 is attracted, the chip 42 itself may be curved, and whenthe sheet 44 is peeled off, the chip 42 may jump off, resulting in apositional deviation which may prevent the suction head from attractingthe chip 42. As a result, when the chip 42 is to be transferred to andplaced in a further process, the chip 42 cannot be positioned withaccuracy. When the chip 42 is curved, it cannot be prevented from beingunduly curved to an unnecessary extent, and hence may be cracked orbroken. If the chip 42 is broken, it is liable to damage the sheet 44,eliminating the vacuum thereby to fail to peel other normal chips 42 offthe sheet 44. Furthermore, when a chip 42 is to be peeled off by thesuction head, a street 59 which lies at the same height as the chip 42may also be peeled off the sheet 44, and attracted and transferredtogether with the chip 42 by the suction head.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a method ofand an apparatus for peeling off chips, which have been attached to asheet and fed therewith, easily and reliably off the sheet for transferto another process.

A major object of the present invention is to provide a method of and anapparatus for peeling chips, which have been attached to a sheet and fedtherewith, off the sheet without damage to the chips while allowing thechips to suffer undesirable positional deviations after the chips havebeen peeled off.

Another object of the present invention is to provide a method of and anapparatus for peeling chips, which have been attached to a sheet and fedtherewith, off the sheet without damage to the sheet while allowingother chips to be peeled reliably off the sheet.

Still another object of the present invention is to provide a method ofand an apparatus for peeling chips off a sheet without the possibilityof peeling off streets attached to the sheet between the chips.

Yet still another object of the present invention is to provide a methodof and an apparatus for peeling chips, which have been attached to asheet and fed therewith, off the sheet efficiently within a short periodof time.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a chip peeling apparatus according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line II--II of FIG. 1;

FIG. 3 is an enlarged fragmentary plan view of the chip peelingapparatus shown in FIG. 1;

FIG. 4 is an enlarged vertical cross-sectional view of the chip peelingapparatus shown in FIG. 1;

FIG. 5 is an enlarged vertical cross-sectional view of the chip peelingapparatus shown in FIG. 1 and a wafer placed thereon;

FIG. 6 is an enlarged vertical cross-sectional view showing the mannerin which the chip peeling apparatus shown in FIG. 1 operates, withportions of a sheet and streets being lowered;

FIG. 7 is an enlarged vertical cross-sectional view showing the mannerin which the chip peeling apparatus shown in FIG. 1 operates, with thesheet and chips being curved;

FIG. 8 is an enlarged vertical cross-sectional view showing the mannerin which the chip peeling apparatus shown in FIG. 1 operates, with chipspeeled off the sheet;

FIG. 9 is an enlarged vertical cross-sectional view showing the mannerin which the chip peeling apparatus shown in FIG. 1 operates, with achip peeled off the sheet and then attracted by a suction head;

FIG. 10 is an enlarged vertical cross-sectional view of a conventionalchip peeling apparatus;

FIG. 11 is an enlarged vertical cross-sectional view showing the mannerin which the conventional chip peeling apparatus illustrated in FIG. 10operates; and

FIG. 12 is an enlarged vertical cross-sectional view of anotherconventional chip peeling apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 show a chip peeling apparatus 60 according to anembodiment of the present invention.

As shown in FIGS. 1 and 2, the chip peeling apparatus 60 includes asubstantially square base 62 having a pair of pins 64a, 64b verticallymounted on an upper surface thereof. As shown in FIG. 2, the base 62 hasa chamber 66 defined therein and a pair of horizontal passages 68a, 68bdefined therein which are held in communication with the chamber 66. Thepassage 68a is connected through a coupling 70 to a vacuum pump 72, andthe passage 68b is connected to a bushing 74, to which the coupling ofanother chip peeling apparatus can be connected. Therefore, a pluralityof chip peeling apparatus 60 may be connected in series with each otherand coupled to the single vacuum pump 72.

The base 62 also has a large-diameter upwardly open circular hole 78defined therein which communicates with the chamber 66 with a horizontalstep 76 extending therebetween. The step 76 has a circular groove 80defined in its upper surface in surrounding relation to the chamber 66,with an annular O-ring 82 fitted in the groove 80. A circular seat 84 isfitted in the hole 78 and fastened to the base 62 by a screw 86. Theseat 84 has an upwardly open circular recess 88 defined therein partlyby a bottom which has a central hole 90 communicating with the chamber66. The bottom which defines the circular recess 88 has a plurality ofconcentric annular ridges 91 disposed on its upper surface. A circularsupport base 92 is fitted in the recess 88 and supported on the annularridges 91. The support base 92 is fastened to the seat 84 by a screw 93.The support base 92 also has a circular step 95 disposed on its uppersurface and extending in the vicinity of an outer circumferential edgethereof, with a flat surface 97 lying radially inwardly of the step 95.The support base 92 further includes a substantially central hole 94defined therein, with a peeling base 98 fitted in the hole 94.

The peeling base 98 will be described in detail below. As shown in FIGS.3 and 4, the peeling base 98 has a plurality of closely positionedupward protrusions 100 each in the form of a quadrangular pyramid on itsupper surface. The protrusions 100 include first protrusions 100a havinga height h₁ and second protrusions 100b having a height h₂ which issmaller than the height h₁. The difference t₂, between the heights h₁,h₂ is equal to or smaller than a sheet thickness t₂ described later on.The first protrusions 100a are positioned so as to be aligned withrespective corners 103a ˜103d of chips 102 (described later on), and thesecond protrusions 100b are positioned in other regions. For example, ifchips 102 are of a substantially square or rectangular shape, then thefirst protrusions 100a are positioned so as to abut against the fourcorners 103a ˜103d of the chips 102.

As shown in FIG. 4, the peeling base 98 has a plurality of holes 106defined vertically therein which communicate with grooves 104 that aredefined between certain protrusions 100 and protrusions 100 adjacentthereto. The holes 106 communicate with the hole 90 defined in the seat84. Therefore, the grooves 104 communicate with the vacuum pump 72through the hole 90, the chamber 66, the passage 68a, and the coupling70. Each of the holes 106 is positioned in the vicinity of the center ofone of the chips 102.

A holder plate 107 and a suction head 108 are disposed above the peelingbase 98 for movement toward and away from the peeling base 98 by anactuator (not shown). The holder plate 107 is made of an electricallyconductive material, and can be moved to a position that is spaced fromthe chips 102 by a distance equal to or smaller than the thickness t₃ ofthe chips 102. The suction head 108 has an axial hole 109 definedtherein which communicates with a vacuum source (not shown).

A wafer retainer plate 110 for being mounted on the chip peelingapparatus 60 will be described below.

As indicated by the two-dot-and-dash lines in FIGS. 1 and 2, the waferretainer plate 110 is of a substantially circular shape and has aplurality of linear edges 111a, 111b, 111c, 111d in respective90°-spaced positions. The wafer retainer plate 110 has recesses 112a,112b defined in outer circumferential edges thereof one on each side ofthe linear edge 111b. When wall surfaces which define the recesses 112,112b engage the pins 64a, 64b of the chip peeling apparatus 60, thewafer retainer plate 110 is positioned with respect to the chip peelingapparatus 60. The wafer retainer plate 110 has a step 113 defined in alower surface thereof for engagement with the step 95 of the supportbase 92. The wafer retainer plate 110 has a substantially rectangularhole 114 defined centrally therein by walls having a plurality ofinwardly projecting teeth 116.

As shown in FIG. 5, an ultraviolet radiation absorbing, flexible sheet(hereinafter referred to as a "UV sheet") 126 having a thickness t₂ isattached to the lower surface of the wafer retainer plate 110. Asubstantially square wafer 118 of silicon or the like is disposed in thehole 114 and held against an upper surface of the UV sheet 126.

As shown in FIGS. 3 through 5, the wafer 118 has a plurality of squarechips 102 and a plurality of elongate rectangular streets 122 remainingas cut fragments in gaps between the chips 102. The wafer 118 also has atab 124 on its outer peripheral edges in surrounding relation to thechips 102. The streets 122 and the tab 124 are unwanted parts that areproduced in a process of fabricating the chips 102, and will bediscarded after the chips 102 are fabricated.

Operation of the chip peeling apparatus 60 in relation to a chip peelingmethod will be described below.

As shown in FIGS. 1 and 2, the wafer retainer plate 110 which is holdingthe wafer 118 is placed on the chip peeling apparatus 60. The wafer 118is positioned with respect to the chip peeling apparatus 60 by bringingthe walls of the recesses 112a, 112b into engagement with the pins 64a,64b. At this time, as shown in FIG. 3, the first protrusions 100a havetheir tops held in abutment against the UV sheet 126 on the reverse sideof the chips 102 in the vicinity of the four corners 103a˜103d of thechips 102, thus supporting the chips 102. As shown in FIG. 4, the topsof the second protrusions 100b are spaced from the UV sheet 126 by thedistance t₁ which is equal to or smaller than the thickness t₂ of the UVsheet 126. The streets 122 are positioned between first protrusions 100aand first protrusions 100a adjacent thereto, and are not supported bythe first protrusions 100a or the second protrusions 100b. As shown inFIGS. 3 and 5, the tab 124 is positioned over the flat surface 97, andin intimate contact therewith through the UV sheet 126.

When the vacuum pump 72 is actuated, air in the grooves 104 isdischarged through the holes 106, the hole 90, and the passage 68a,lowering the air pressure in the grooves 104. As shown in FIG. 6, the UVsheet 126 is stretched into the grooves 104 under a vacuum, lowering thestreets 122 which are not supported by the protrusions 100. The UV sheet126 is now peeled off the edges of the chips 102. Since the streets 122descend with the UV sheet 126 at this time, the streets 122 are notpeeled off the UV sheet 126.

Upon continued attraction of the UV sheet 126, the central areas of thechips 102 are curved downwardly, as shown in FIG. 7. When the centralareas of the chips 102 are curved to a given extent, the central areasof the chips 102 abut against and are supported by the tops of thesecond protrusions 100b, preventing the chips 102 from being curvedfurther downwardly. Since the curved chips 102 are subjected to forcestending to recover them, the chips 102 gradually restore their originalshape, allowing the UV sheet 126 to be gradually peeled off the chips102. On the tops of the second protrusions 100b, the UV sheet 126remains attached to the chips 102 until the chips 102 return to theiroriginal flat shape, when the UV sheet 126 is peeled off the chips 102on the tops of the second protrusions 100b, as shown in FIG. 8.

Since the chips 102 are slightly curved as they are supported on thesecond protrusions 100b, the forces tending to recover the chips 102 aresmall. Consequently, the chips 102 do not jump off or are notpositionally deviated when the UV sheet 126 is peeled off the chips 102.If the forces tending to recover the chips 102 are relatively large dueto their shape or other factors, the chips 102 may possibly jump off.However, the holder plate 107 is effective in preventing the chips 102from unduly jumping off, and hence preventing them from beingpositionally deviated. Inasmuch as the holder plate 107 is made of anelectrically conductive material, the chips 102 are not attracted to theholder plate 107 because of electrostatic charges which are developedwhen the UV sheet 126 is peeled off the chips 102.

Because the UV sheet 126 is prevented from being unduly stretched by theabutment against the second protrusions 100b, the UV sheet 126 isprotected against damage. Since the UV sheet 126 is not damaged, thevacuum created in the grooves 104 is securely maintained, avoiding thepossibility of an undesirable peel-off failure of the chips 102. Ifadjacent chips 102 are peeled off the UV sheet 126 at different times,then the UV sheet 126 is subject to a horizontal force tending to movethe UV sheet 126 horizontally. However, since the UV sheet 126 is heldagainst the tops of the first and second protrusions 100a, 100b, the UVsheet 126 is prevented from being moved horizontally even under such ahorizontal force, thus preventing the chips 102 from being positionallydeviated.

Then, the holder plate 107 is displaced away from the chips 102, and thesuction head 108 is lowered into abutment against one of the chips 102.The vacuum source connected to the suction head 108 is actuated toattract the chip 102 to the suction head 108. The suction head 108 isthen elevated. Since the UV sheet 126 is attached to the chip 102through a small area on the tops of the corresponding first protrusions100a, the chip 102 is peeled off the UV sheet 126 with a small force,and held by the suction head 108, as shown in FIG. 9. The suction head108 then carries the chip 102 to a next process.

The chips 102 will successively be peeled off the UV sheet 126 in themanner described above. Since the streets 122 are not peeled off the UVsheet 126, the streets 122 will not be delivered to the next process.

The tab 126 is held in intimate contact with the upper surface of theflat surface 97 through the UV sheet 126, as described above. Therefore,the tab 126 will not be peeled off the UV sheet 126.

A peeling test was conducted on the chips 102 using the chip peelingmethod and the chip peeling apparatus 60 described above. Details andresults of the peeling test will be described below with respect toexperimental and comparative examples.

EXPERIMENTAL EXAMPLE

In the chip peeling apparatus 60, the tops of adjacent ones of theprotrusions 100 of a peeling base 98a were spaced 2.63 mm in an X-axisdirection and 3.12 mm in a Y-axis direction. Four first protrusions 100aand five second protrusions 100b were closely positioned in a squarepattern as shown in FIG. 3. Specifically, the first protrusions 100awere positioned in alignment with the four corners 103a˜103d of a chip102, and the second protrusions 100b were positioned in other regions.

A wafer 118 was placed on the chip peeling apparatus 60, and the vacuumpump 72 was actuated to peel the UV sheet 126. The time required forpeeling the UV sheet 126, the positional deviation which the chip 102suffered when the UV sheet 126 was peeled, the frequency with which thechip 102 was skewed when the UV sheet 126 was peeled, the frequency withwhich the chip 102 jumped when the UV sheet 126 was peeled, and thefrequency of peeling failures between the UV sheet 126 and the chip 102were measured.

COMPARATIVE EXAMPLE

Peeling bases 98b˜98d with protrusions 100 of equal height wereproduced. On the peeling base 98b, the tops of adjacent ones of theprotrusions 100 were spaced 3 mm in the X-axis direction and 3 mm in theY-axis direction. On the peeling base 98c, the tops of adjacent ones ofthe protrusions 100 were spaced 2.5 mm in the X-axis direction and 2.5mm in the Y-axis direction. On the peeling base 98d, the tops ofadjacent ones of the protrusions 100 were spaced 1.94 mm in the X-axisdirection and 2.34 mm in the Y-axis direction. The number of protrusions100 for supporting one chip 102 was 9 on the peeling base 98b, 16 on thepeeling base 98c, and 16 on the peeling base 98d. The time required forpeeling the UV sheet 126, the positional deviation which the chip 102suffered when the UV sheet 126 was peeled, the frequency with which thechip 102 was skewed when the UV sheet 126 was peeled, the frequency withwhich the chip 102 jumped when the UV sheet 126 was peeled, and thefrequency of peeling failures between the UV sheet 126 and the chip 102were also measured with respect to these peeling bases 98b, 98c, 98d.

The results of the peeling test are shown in Table below.

                                      TABLE                                       __________________________________________________________________________              Distance between Frequency                                                                          Frequency                                                                          Frequency                                          protrusions                                                                           Peeling                                                                           Positional                                                                         of   of   of peeling                                         X-axis                                                                            Y-axis                                                                            time                                                                              deviation                                                                          skews                                                                              jumps                                                                              failures                                           [mm]                                                                              [mm]                                                                              [sec.]                                                                            [mm] [%]  [%]  [%]                                      __________________________________________________________________________    Inv. Ex.                                                                           Peeling                                                                            2.63                                                                              3.12                                                                               15 0    0    0    0                                             base 98a                                                                 Com. Ex.                                                                           Peeling                                                                            3.0 3.0  60 0.06 7.3  2.0  0                                             base 98b                                                                      Peeling                                                                            2.5 2.5 100 0.10 12.2 2.0  0                                             base 98c                                                                      Peeling                                                                            1.94                                                                              2.34                                                                              300 or                                                                            0    1.5  0    13.3                                          base 98d     longer                                                      __________________________________________________________________________

It can be seen from the above test results that the chip peelingapparatus 60 according to the present invention had a short peelingtime, suffered no positional deviation of the chip 102, and did notcause the chip 102 to be skewed, jump, and suffer a peeling failure.

With the peeling bases 98b, 98c according to the comparative example,however, the peeling time was long, the chip 102 suffered a positionaldeviation, was skewed, and jumped though no peeling failure occurred.With the peeling base 98d, the chip 102 suffered no positional deviationand did not jump, but the peeling time was quite long and the frequencyof peeling failures was high.

The chip peeling method and the chip peeling apparatus according to thepresent invention offer the following advantages:

The chips are prevented from being damaged by needles which wouldotherwise be employed in the conventional chip peeling apparatus. Whenthe chips are curved, they are supported by the second protrusions andhence prevented from being further curved. Therefore, the chips areprevented from being cracked or broken, and the sheet is protectedagainst damage, preventing peeling failures which would otherwise takeplace due to the elimination of the vacuum needed to peel the chips offthe sheet. Since forces tending to recover the chips are small, thechips do not suffer a possibility of positional deviations. Even if thechips are subject to large restoring forces, they are prevented fromjumping off by the holder plate, and hence from being positionallydeviated. Inasmuch as the time required to peel off the chips can beshortened, the chips can be peeled off the sheet with improvedefficiency.

Although a certain preferred embodiment of the present invention hasbeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

What is claimed is:
 1. A method of peeling a plurality of chips of a wafer off a flexible sheet attached to a reverse side of said wafer, said method comprising the steps of:placing a wafer retainer plate that holds said wafer with said plurality of chips on a plurality of first protrusions and second protrusions that are integrally formed with a peeling plate and that have different heights, wherein the difference in height between said first and second protrusions is equal to or smaller than the thickness of said flexible sheet and further wherein said peeling plate has suction holes between said first protrusions and said second protrusions positioned next to said first protrusions, drawing said flexible sheet under a vacuum through said suction holes thereby to curve said flexible sheet due to the different heights of the first protrusions and the second protrusions, said drawing thereby peeling the chips off said flexible sheet; and attracting and carrying the chips peeled off said flexible sheet.
 2. A method according to claim 1, further comprising the step of:holding said chips with a holder plate when the flexible sheet is drawn under the vacuum.
 3. A method according to claim 1, wherein said first protrusions are configured to be aligned with the corners of the chips to be peeled. 